M900 Aluminium Swingarm

[Nasher]

I purchased this swingarm with the plan to design and weld on an underslung brace - all very 1990's!

I've since purchased another one which is in worse condition, and won't be such a sacrifice both in monetary terms and morally if I c**k it up.

It's in quite good condition, but does have some damage as shown in the images.
Not that clear is that one of the chain adjuster end plates has the inside edge shaved off, I'm assuming by a sprocket bolt head or similar.

I was going to weld on a brace, the vapour blast it and either get it re anodised or just clear lacquer it.

It is of course perfectly useable in it's current state.











I'm looking for £150 for it, plus postage within the UK of £10.
Or it can be collected from South Hampshire.

Nasher

[Mr Gazza]

Good luck with the sale Nasher.
These alloy arms don't come up for sale very often. We now know from a recent thread that all the swinging arms on hoop models are interchangeable. So that means that this arm will also fit the M750 and M600. It won't fit the ie models except for the early (2000) M900ie which didn't change to rod suspension link and 25mm axle until 2001.

It's normal for the adjuster plate on the sprocket side to be "shaved" off. This is to clear the sprocket nuts. You can use a shaved one on the right side but not a RH one on the sprocket side.

Also to avoid disappointment; don't attempt to wind out the adjuster bolts from the axle blocks without first removing the tiny screw and washer from the inside end of the bolt. this is there to prevent the bolts from being lost down the road along with the adjuster plates, should they work loose... However it will get mighty noisy before that if it's the sprocket side that comes loose!!

Looks like the marks either side were caused by a clumsily mounted high rise exhaust... They should polish out.

[Nasher]

Thanks Mr G, for the additional info.

Unfortunately the marks on either side are too deep to polish out without trace, but could be made to look a lot nicer.

Nasher.

[350TSS]

Probably too much time on my hands – and it is cold in my North facing garage so my project can sit for a day or two. When you said you wanted to brace the swinging arm my immediate reaction was “Where would I brace it from and to?”
Most of the 80/90s braced SAs had underslung fabrications between the SA pivot point and the rear wheel axle, triangulating that relationship and stiffening them up so the above SA cantilever rear suspension mounts were structurally strengthened.
The M900 arrangement is different as the suspension is arranged so the input force is transmitted via rods and a rocker arm back (via an extremely strong pivot point on the frame) to the SA.
I think the need for bracing on an aluminium M600/750/900 should only be required:
1. between the SA pivot point and the point where the upward force from the wheel is applied to the SA (bottom shock mount), this would be a very tight little triangle and would not be easy to make as the difference between the points where the clamps grip the SA spindle and the centrally mounted shock are greater than the ability to reasonably triangulate given that you will probably have to be using 25mm x 25mm square aluminium tube and the triangle would have to be skewed centrally to the lower shock mount;
2. the point immediately below the hoop mount on the SA directly in line with the reaction required to operate the shock absorber and a line drawn to the centre of the rear axle in its mid adjustment position. On the left hand side this will almost certainly interfere with the chain run so will not be a straight line and therefore not be of optimal strength/ use.
If you made a brace between the rear axle and the bottom shock mount it would reduce any flex between the rear axle mount and the hoop mounting points on the SA (simply by adding extra section against the bending force applied at that point).
The brace could not be a straight line because it would have to accommodate the tyre width and also the chain movement on the left hand side.

Good Luck

[Nasher]

Thanks 350TSS

Can I admit now that I'd only really be doing it out of some kind of period retro fashion statement.



Nasher.

[Mr Gazza]

The swinging arm from an SS model can be used inverted in a Monster.
The structure that attaches the SS monoshock then effectively becomes an underslung brace.
You can trim off the shock mounts for neatness and you also have to add mounting points (rivnuts) to move the chain slipper to the other side.
I've seen this done on a 750SS which was "Nakedized". The builder added lugs for twin shocks, but suitable lugs for the suspension hoop could equally easily be added.

My SS has a steel swinger but I am sure in my mind that there is also an aluminium version, probably only fitted to the 900SS?

[350TSS]

Nasher: That does look good, I do love the 851/888 bikes - I do not think a floating rear brake caliper be possible with that?
Mr Gazza: that is an intriguing solution, if I was contemplating it (which i am not) I think I would ensure that all non used holes were welded up
My 1992 K reg 750SS has an aluminium SA with a welded in solid lug for the rear wheel adjuster - not the compressible box section and cast insert arrangement of the Monster

[Nasher]

Yep, similar to the Monster range the 900SS was fitted with an Aluminium arm and the 400, 600 and 750 a steel one.

I'm (Very Slowly) building up a modified 900SS from parts.
The Aluminium arms are sought after, so I purchased one cheaply that had very crudely had the top brace/shock mount frame filled in with sheet alloy.

After many hours with grinder, dremel,and emery cloth, plus cutting a hole both sides and turning over the edges I've ended up with this.



Does anyone want to make an offer for the monster arm?

Nasher

[350TSS]

That looks factory

[Stafford]

Originally Posted by Nasher

Thanks 350TSS

Can I admit now that I'd only really be doing it out of some kind of period retro fashion statement.



Nasher.

You do realise that that one has a steel swing arm with steel bracing?

[Darkness]

Which are actually lighter, the standard steel, or the standard ally Monster swinging arms?

[Nasher]

Originally Posted by Stafford

You do realise that that one has a steel swing arm with steel bracing?

Yep, But I want to do an Ali one.

[utopia]

I can't put a figure on it but I believe the ally one is lighter, but not by as much as you might think.
I did weigh a few bits when I swapped my steel one for ally a few years ago but unfortunately I never did a comparison between complete assemblies, ie including spindles, chain adjusters etc.
I was left with the impression that there wasn't a lot of difference between the two but that it was still a worthwhile mod both for the relatively small weight loss and also for the improved look.
There are also further opportunities to lose a little more weight by swapping, for example, the steel brake torque pin for titanium, whereas the steel arm has an integral, welded in torque pin which is impossible to lighten.
One of these days I might actually get round to machining up such a lightweight pin. Best laid plans an' all that.

[Dukedesmo]

Mine has a braced swingarm, not sure if Monster or 851/888 but an original Ducati made one.

It was not without problems though as the bracing was very 'tight' on the chain side and the chain sits close to the tyre so I had a problem with the chain bouncing between the two and eating into the bracing.

After repairing it, I made a stainless steel guard plate for the brace but then the 'bouncing' actually cracked the brace where the guard ended so I widened the bracing and all seems much better now.

Also it had similar scarring to the one above but all that can be repaired by welding/grinding etc.

I did keep a spare standard ally swinger that I initially had as a backup if required.

Swingarm (with unsuccessful chain guard in place);





As per Utopia's comments, I don't think there's much weight difference between ally and steel and I would say the braced ally would be heavier? and I'm not sure how much difference the bracing makes to handling etc. but I suspect none that a mere mortal could detect - looks good though!

[Nasher]

Well done DD that looks good.

Thats most likely a M900 arm. The 851/888 ones 'usually' have little vertical brackets welded on to mount the rear hugger.

I'm quite prepared to admit that I want to brace an Ali arm just because I want one.
And I'm not a good enough rider to notice the additional weight, especially at the rear end.

Nasher.